Process for forming on an aluminum surface a colored design

ABSTRACT

A process is disclosed for forming on an aluminum substrate a colored design or pattern. The process comprises printing on the aluminum surface a masking agent or a resist before a first film forming step and then removing the printed agent before a second anodizing step, thereby different colors or shades being produced on a imaged portion and a non-imaged portion of the substrate.

United States Patent Kaneda et al. Oct. 1, 1974 Y PROCESS FOR FORMING ON AN [56] References Cited ALUMINUM SURFACE A COLORED UNITED STATES PATENTS DESIGN 3,284,321 11/1966 Fromson 204/18 R 75 Inventors; Kazuyoshi Kaneda; Yasushi Suzuki, 3,450,606 6/1969 Darrow 204/18 R both of ShiZUOka, Japan OTHER PUBLICATIONS [73] A i Riken Lightmetal Industry Unusual Anodizing Processes and their Practical Sig- Company, Limited, ShiZu ka-Shi, nificance, Electroplating and Metal Finishing Nov. Sizuoka-ken, Japan 1961 pp. 407-415.

[22] Filed: 1972 Primary ExaminerT. M. Tufariello [21] Appl. No.: 285,013

[57] ABSTRACT [30] Foreign Application priority Data A process is disclosed for forming on an aluminum Au 31 1971 Ja an 46 66803 substrate a colored design or pattern. The process 1971 Japan 46-66806 comprises printing on the aluminum surface a masking p agent or a resist before a first film forming step and then removing the printed agent before a second an- C odizing step, thereby different colors or shades being [58] Field 4/15 18 R 29 33 produced on a imaged portion and a non-imaged porb 4 1 tron of the substrate.

5 Claims, N0 Drawings PROCESS FOR FORMING ON AN ALUMINUM SURFACE A COLORED DESIGN This invention relates to a process for forming on an aluminum or aluminum alloy surface an attractively colored design a pattern without the addition of any coloring dyes and pigments. More specifically, the present invention is concerned with the process in which a masking'agent or a resist is printed or coated on an aluminum surface before a first film forming step and then removed before a second anodizing step.

There have hitherto been proposed a variety of processes for producing a colored design a pattern on the aluminum or aluminum alloy surface, for example, Japanese Patent Publications No. 34-3863 and No. 44-9804 wherein various dyes and pigments are adsorbed into the fine pores or cavities which develop in the surface when anodized. Although this process has the advantage that a colored design having an extensive color range has formed on the aluminum surface, the formed color is inevitably faded or discolored due to poor durability thereof.

It is also well known that an ornamental colored film has been produced on an aluminum surface by anodization or chemical conversion treatment. There has been also disclosed a process for producing a colored design or pattern on an aluminum surface in which a masking agent or a resist is printed or coated on the surface after a first film forming step and then removed after a second film forming step. This prior art process necessarily requires an etching step before the second film forming step. Due to the presence of the etching step, the aluminum surface treated according to this process has a very limited color range, the corrosion resistance thereof unfavorably decreases, and the treatment cost involved increses wastefully.

It is the primary object of this invention to provide a novel process for producing on an aluminum surface a protective ornamental film having a colored design which process will eliminate the foregoing difficulties of the various prior-art processes. It is a more specific object of the invention to provide a novel, simple and economical process wherein anodization incorporates with chemical conversion treatment to form at a low cost a protective and abrasion resistant film together with a colored design or pattern having an extensive color range.

Briefly stated, the inventive concept of this invention resides in a process which comprises degreasing, cleaning and water-rinsing an aluminum surface, etching the water-rinsed surface with an alkaline solution, neutralizing and water-washing the etched surface, printing or coating a masking agent or a resist on the surface, subjecting the surface to a first film forming step, removing the printed masking agent, anodizing the surface and water-rinsing the surface.

The masking agent or a resist used herein is mainly composed of a synthetic resin having acid resistance and alkali resistance and may be printed or coated on an aluminum surface with the use of a screen printing machine, coater or any other means.

The first film forming treatment is effected in order to form a non-porous oxidized film such as a barrier film, a boehmite film or a chemical conversion coating on a non-printed or non-imaged portion of an aluminum surface. The barrier film is formed by a conventional process such as wherein an aluminum surface is immersed in a bath containing aromatic sulfonic acids, having no sulfate ion, chromic acid, malonic acid and the like while the voltage is rapidly charged from O to 60 volts in less than 60 seconds. As the thickness of the barrier film developed on the surface is enough in a degree that a colored design is without difficulty produced in a second anodizing step described later, the treatment time is satisfactorily within one minute. The boehmite film is produced by immersing an aluminum surface in boiling distilled or desalted water in more than 3 minutes. The chemical conversion coating according to this invention is formed by immersing the aluminum surface for at least 5 minutes in distilled water or desalted water containing 01-10 percent of an organic amine selected from the group consisting of dimetyl ethanol amine, monoethanol amine, mononormal-propyl amine, tetraethylene pentamine and ethylene diamine heated at 4050C.

After the above described first treatment, the printed masking agent is dissolved with an organic solvent, thereby the pretreated aluminum surface being exposed in the air.

Then the aluminum surface is anodized to form a colored anodized film on the imaged portion thereof. The imaged surface turns gold, bronze, silver white or any other colors in accordance with the composition of an anodizing bath such as oxalic acid, sulfuric acid, chromic acid or any other chemicals. In this anodization the imaged surface is rapidly anodized and colored deeply but the non-imaged surface is anodized more slowly in comparison with the imaged surface due to the presence of a barrier film, a boehmite film or a chemical conversion coating formed thereon to be colored lightly. The aluminum surface, if desired, may be anodized further in a different bath to produce on the nonimaged surface a different colored film from the one on the imaged surface.

According to this invention the imaged surface may be colored as desired without change of color of the non-imaged surface because conditions of anodization may be changeable in harmony with the first treatment.

In the practical use of this invention, an aluminum substrate is as a matter of course degreased, washed, neutralized, washed again and dried before printing a masking agent and dried again after printing and then after the final anodizing process the surface is washed, porosity-sealed and coated according to the conventional processes.

Thus, in accordance with the invention, various colorful building materials, household articles and the like can be provided. Abrasion resistance and corrosion resistance may be improved owing to the formation of a thick protective film. It has been found that the imaged surface has good durability and can be used for a long time without discoloration.

The following examples are provided to further illustrate the process of the present invention, but these are not to be regarded as limiting.

EXAMPLE I An aluminum-bearing substrate was subjected to the pretreatment in which it was degreased and cleaned by dipping for 30 seconds in a 5 percent NaOH solution at a room temperature; washed again with water; and dried in the air.

Then on the pretreated substrate a design was printed with an acid and alkali resistant masking agent composed mainly of synthetic resins and the printed agent was dried. The substrate was subjected to anodization using a 5 wt percent cresol sulfonic acid having no sulfate ion electrolyte operated under the condition that a DC voltage was rapidly charged from to 60 volts at a current density of 2 A/dm at a bath temperature of 20C. The substrate was thus anodized for 40 seconds, thereby a non-porous film (a barrier film) being produced on the aluminum surface except the printed or imaged surface. Then the printed masking agent was removed with absorbent cotton having an organic solvent, thereby the printed or imaged pretreated aluminum surface being exposed in the air. Further the substrate was subjected to anodization using a 3 wt percent oxalic acid electrolyte operated with a DC 50-65 volts source at a current density of 2 A/dm at a bath temperature of 20C. The substrate was thus anodized for 45 minutes. The imaged surface of the substrate turned deep gold in color and the remaining or non-imaged surface thereof light gold.

EXAMPLE II An aluminum-bearing substrate was pretreated in the manner described in EXAMPLE I. A design was printed on the substrate with the same agent as described in EXAMPLE I and the printed agent was dried. The substrate was subjected to anodization using a 3 wt percent chromic acid electrolyte operated under the same condition as described in EXAMPLE I and then the masking agent was removed in the manner described in EXAMPLE I. Further the substrate was subjected to anodization using a wt percent cresol sulfonic acid containing 0.15 wt percent sulfuric acid electrolyte operated with a DC 50 volts source at a current density of 1 A/dm at a bath temperature of 20C. The substrate was thus anodized for 45 minutes. The imaged surface of the substrate turned deep bronze and the remaining or non-imaged surface thereof light bronze.

EXAMPLE III An aluminum-bearing substrate was pretreated in the manner described in EXAMPLE I. A design was printed on the substrate with the same agent as described in EXAMPLE I and the printed agent was dried. The substrate was subjected to anodization using a 3 wt percent malonic acid electrolyte operated under the same condition as described in EXAMPLE I and then the masking agent was removed in the manner de scribed in EXAMPLE I. Further the substrate was subjected to anodization using a 5 wt percent sulfosalicylic acid containing 0.15 wt percent sulfuric acid electrolyte operated under the same condition as described in EXAMPLE II. The substrate was thus anodized for 30 minutes, thereby only the imaged surface of the substrate turning bronze in color. Then the substrate was subjected to anodization using a wt percent sulfuric acid electrolyte operated with a DC 15 volts source at a current density of l A/dm at a bath temperature of C. The substrate was anodized for 30 minutes. The remaining or non-imaged surface of the substrate turned silver white in color.

EXAMPLE IV An aluminum-bearing substrate was pretreated in the manner described in EXAMPLE I. A design was printed on the substrate with the same agent as described in EXAMPLE I and the printed agent was dried. The substrate was subjected to anodization using a 3 wt percent malonic acid electrolyte operated under the same condition as described in EXAMPLE I and then the masking agent was removed in the manner described in EXAMPLE I. Further the substrate was subjected to anodization using a 5 wt percent phenol sulufonic acid containing 0.15 wt percent sulfuric acid operated under the same condition described in EXAM- PLE II. The substrate was thus anodized for 30 minutes, thereby only the imaged surface of the substrate turning bronze in color. Then the substrate was subjected to anodization using a 3 wt percent oxalic acid electrolyte operated with a DC 65 volts source at a current density of 2 A/dm at a bath temperature of 20C. The substrate was anodized for 30 minutes. The remaining or non-imaged surface of the substrate turned gold in color.

EXAMPLE V An aluminum-bearing substrate was pretreated in the manner described in EXAMPLE I. A design was printed on the substrate with the same agent as described in EXAMPLE I and the printed agent was dried. The substrate was immersed in boiling distilled water for 5 minutes, thereby a boehmite film being produced on the ground or non-imaged surface of the substrate. Then the masking agent was removed with absorbent cotton containing an organic solvent. The substrate was subjected to anodization using a 5 wt percent cresol sulfonic acid containing 0.15 wt percent sulfuric acid electrolyte operated with a DC 50 volts source at a current density of 1 A/dm at a bath temperature of 20C. The substrate was thus anodized for 15 minutes. The imaged surface of the substrate turned bronze in color and the ground or non-imaged surface thereof had a color peculiar to the aluminum substrate.

EXAMPLE VI A boehmite film was produced on an aluminumbearing substrate in the manner described in EXAM- PLE V. The masking agent was removed in the same manner as described in EXAMPLE V. The substrate was subjected to anodization using a 3 wt percent oxalic acid electrolyte operated with a DC 50-65 volts source at a current density of 2 A/dm at a bath temperature of 20C. The substrate was anodized for 45 minutes. The imaged surface of the substrate turned deep gold in color and the ground or non-imaged surface thereof had a color peculiar to the aluminum substrate.

EXAMPLE VII A boehmite film was produced on an aluminumbearing substrate in the manner described in EXAM- PLE V. The substrate was subjected to anodization using a 5 wt percent cresol sulfonic acid containing 0.15 wt percent sulfuric acid electrolyte operated with a DC 50 volts source at a current density of l A/dm at a bath temperature of 20C. The substrate was anodized for 45 minutes. The imaged surface of the substrate turned deep bronze in color and the ground or non-imaged surface thereof had a color peculiar to the aluminum substrate.

EXAMPLE VIII A boehmite film was produced on an aluminumbearing substrate in the manner described in EXAM- PLE V. The substrate was subjected to anodization using a 5 wt percent sulfosalicylic acid containing 0.15 wt percent sulfuric acid electrolyte operated under the same condition as described in EXAMPLE VII. The substrate was thus anodized for 30 minutes, thereby the imaged surface thereof turning bronze in color. Further the substrate was subjected to anodization using a 15 wt percent sulfuric acid electrolyte operated with a DC 15 volts source at a current density of 1 A/dm at a bath temperature of 20C. The substrate was anodized for 30 minutes. The ground or non-imaged surface thereof turned silver white in color and the imaged surface was still bronze.

EXAMPLE IX A boehmite film was produced on an aluminumbearing substrate in the manner described in EXAM- PLE V. The substrate was subjected to anodization using a 5 wt percent phenol sulfonic acid containing 0.15 wt percent sulfuric acid electrolyte operated under the same condition as described in EXAMPLE VII. The substrate was thus anodized for 30 minutes, thereby the imaged surface thereof turning bronze in color. Further the substrate was subjected to anodization using a 3 wt percent oxalic acid electrolyte operated with a DC 65 volts source at a current density of 2 A/dm at a bath temperature of 20C. The substrate was thus anodized for 30 minutes, The ground or nonimaged surface thereof turned gold in color and the imaged surface was still bronze.

EXAMPLE X An aluminum substrate was pretreated in the manner described in EXAMPLE I. A design was printed on the sustrate with the same agent as described in EXAM- PLE I and the printed agent was dried. The substrate was immersed in distilled water containing a small amount of ETHODUOMEEN (trade name for ethylene oxide adduct of fatty acid diamine) at a PH within the range of 8 to 10 and at a temperature within the range of 60 to 70C for ten minutes, thereby a bronze chemical conversion film being produced on the ground or non-imaged surface of the substrate. Then the printed resist-film was removed with an organic solvent. Further the substrate was subjected to anodization using a wt percent sulfuric acid electrolyte operated with a DC 50 volts source at a current density of l A/dm at a temperature of 20C. The substrate was anodized for 15 minutes. The imaged surface of the substrate turned silver white in color and the ground or non-imaged surface was still bronze.

What is claimed is:

l. A process for forming on an aluminum or aluminum alloy surface a colored design or pattern which comprises: degreasing, cleaning and water-rinsing the surface; etching the water-rinsed surface with an alkaline solution; neutralizing and water-washing the etched surface; printing or coating a masking agent on the surface; forming on said surface a substantially completely exposed thin non-porous barrier layer by anodizing the thus pretreated surface for less than 60 seconds; removing the masking agent and then anodizing the surface.

2. The process for forming on an aluminum or aluminum alloy surface a colored design or pattern as defined in claim 1, which further comprises anodizing the anodized surface in a different bath.

3. A process for forming on an aluminum or aluminum alloy surface a colored design or pattern which comprises; degreasing, cleaning and water-rinsing the surface; etching the water-rinsed surface with an alkaline solution; neutralizing and water-washing the etched surface; printing or coating a masking agent on the surface; forming on said surface a boehmite film by immersing the thus pretreated surface in boiling water; removing the masking agent and then anodizing the surface.

4. The process for forming on an aluminum or aluminum alloy surface a colored design or pattern as defined in claim 3, which further comprises anodizing the anodized surface in a different bath.

5. A process for forming on an aluminum or aluminum alloy surface a colored design or pattern which comprises: degreasing, cleaning and water-rinsing the surface; etching the water-rinsed surface with an alkaline solution; neutralizing and water-washing the etched surface; printing or coating a masking agent on the surface; immersing the surface for at least 5 minutes in distilled water or desalted water containing 01-10 percent of an organic amine selected from the group consisting of dimethyl ethanol amine, monoethanol amine, triethanol amine, mono-normal-propyl amine, tetraethylene pentamine and ethylene diamine heated at 40 C; removing the masking agent and anodizing the surface. 

1. A PROCESS FOR FORMING AN ALUMINUM OR ALUMINUM ALLOY SURFACE A COLORED DISIGN OR PATTERN WHICH COMPRISES: DEGREASING, CLEANING AND WATER-RINSING THE SURFACE; ETCHING THE WATERRINSED SURFACE WITH AN ALKALINE SOLUTIONL NUTRALIZING AND WATER-WASHING THE ETCHED SURFACE; PRINTING OR COATING A MASKING AGENT ON THE SURFACE; FORMING ON SAID SURFACE A SUBSTANTIALLY COMPLETELY EXPOSED THIN NON-POROUS BARRIER LAYER BY ANODIZING THE THUS PRETREATED SURFACE FOR LESS THAN 60 SECONDS; REMOVING THE MASKING AGENT AND THEN ANODIZING THE SURFACE.
 2. The process for forming on an aluminum or aluminum alloy surface a colored design or pattern as defined in claim 1, which further comprises anodizing the anodized surface in a different bath.
 3. A process for forming on an aluminum or aluminum alloy surface a colored design or pattern which comprises; degreasing, cleaning and water-rinsing the surface; etching the water-rinsed surface with an alkaline solution; neutralizing and water-washing the etched surface; printing or coating a masking agent on the surface; forming on said surface a boehmite film by immersing the thus pretreated surface in boiling water; removing the masking agent and then anodizing the surface.
 4. The process for forming on an aluminum or aluminum alloy surface a colored design or pattern as defined in claim 3, which further comprises anodizing the anodized surface in a different bath.
 5. A process for forming on an aluminum or aluminum alloy surface a colored design or pattern which comprises: degreasing, cleaning and water-rinsing the surface; etching the water-rinsed surface with an alkaline solution; neutralizing and water-washing the etched surface; printing or coating a masking agent on the surface; immersing the surface for at least 5 minutes in distilled water or desalted water containing 0.1-10 percent of an organic amine selected from the group consisting of dimethyl ethanol amine, monoethanol amine, triethanol amine, mono-normal-propyl amine, tetraethylene pentamine and ethylene diamine heated at 40* - 90*C; removing the masking agent and anodizing the surface. 